Single level spine fusion procedure typically entails removing the intervertebral disk (not shown) and inserting an interbody device into the disk space.
Current spine fusion procedures rely heavily on the use of posterior fixation to achieve the stability and rigidity necessary to obtain successful clinical results. However, implantation of posterior instrumentation necessarily involves removing important musculoskeletal elements.
Because of these concerns, anterior fixation systems have also been developed which require removal of much less musculoskeletal mass. However, because anterior fixation, especially in the abdominal or thoracic area, lies in close proximity to vital internal organs such as the aorta, these fixation systems must also possess a low profile.
In general, conventional intervertebral connection systems can be characterized by ligament components which are either a) relatively rigid, or b) not shaped for cooperative connection to bone fasteners, or by bone fasteners which are shouldered to seat upon the vertebral surface. When the ligament is relatively rigid, it must essentially fully lie upon the anterior surfaces of the adjacent vertebrae, thereby limiting design options. Systems having relatively rigid ligaments typically have transverse holes near their end portions for accepting bone fasteners. In systems in which the ligament is not shaped for cooperative attachment to the bone fastener, attachment is typically made by either suturing or by passing a screw through the ligament. When the bone fastener is seated upon the vertebral surface, a portion of the bone fastener protrudes from the surface and the tension of the ligament can not be further adjusted.
US Patent Application No. 2002/0143329 (“Serhan”) discloses a system in which a ligament has conformable portions and end portions shaped to cooperatively connect to shoulderless bone fasteners. The shoulderless feature of the bone fastener allows the bone fastener to be fully driven into the vertebral surface, thereby eliminating any problematic protrusion while also providing a means to adjust the tension of the ligament after the bone fasteners have been located. The conformable portions of the ligament allow the ligament to conform to the recess produced by a fully driven bone fastener without generating undue stress, thereby accommodating the surgeon's desire to fully drive the bone fastener within the recess. The cooperative shape of the ligament end portions allows for non-destructive attachment of the ligament to the bone fasteners without the use of sutures, thereby minimizing unwanted connection-related stresses and undesirable generation of foreign particles within the patient.
However, in many embodiments disclosed in Serhan, the bone fasteners are fixed to the bone by impaction. These impaction forces may compromise the integrity of the bone fastener component.
Moreover, the system disclosed in Serhan requires that the surgeon insert the system under tension and set or hold the tension while deploying the anchoring system. This makes the implantation procedures very arduous, and, due to high impaction forces, may not be suitable for use in certain areas of the spine.